In Firefox, I had bookmarks with keywords, so I could easily search for stuff. When I imported these bookmarks to Chrome - keywords still work. But when adding new bookmark, I can't find a way to define its keyword.

Could you give an example of how and where you use those keywords?. Because can do shift+ctrl+o to open the bookmarks manager which has a search box. You can also replace the name of the bookmark. Also the omnibox itself suggests from your bookmarks.
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Martín CanavalJan 22 '13 at 18:23

Kayword is a special word that can be used for accessing given bookmark. It can also modify URL. Example on usage in Firefox can be found in here: depesz.com/2007/09/26/…
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user7385Jan 22 '13 at 18:29

Using Omnibox and the multiple search engines provided by Chrome, you can add, for example a custom one for the ArchWiki (If it wasn't added automatically), just like the one in the picture below, with a nice and short keyword. In my case aw.

So now, each time I want to search something on the ArchWiki, I just go to the omnibox, type aw and then hit tab (or space) and the custom search engine switches temporarily to ArchWiki, allowing me to quickly search directly there and even takes me to the appropriate page if the term is accurate enough.

// If you are wondering how the custom ArchWiki ended up in the top box, it's because I accidentally made it the default search engine.